What I tell you three times is true
Note: Portions of this chapter originally appeared, in considerably different form, in my book Date on Database: Writings 2000-2006 (Apress, 2006).
Redundant adj. de trop, diffuse, excessive, extra, inessential, inordinate, padded, periphrastic, pleonastical, prolix, repetitious, supererogatory, superfluous, supernumerary, surplus, tautological, unemployed, unnecessary, unneeded, unwanted, verbose, wordy
I give the foregoing splendid list of synonyms here purely for whatever intrinsic interest it might have (I found it in Chambers Twentieth Century Thesaurus, which also gives the following nice list of antonyms: concise, essential, necessary). Be that as it may, we’ve seen that design theory in general can be regarded as a set of principles and techniques for reducing redundancy (and thereby reducing the potential for certain inconsistencies and update anomalies that might otherwise occur). But what exactly is redundancy? We don’t seem to have a very precise definition of the term; we just have a somewhat vague idea that it can lead to problems, at least if it isn’t managed properly.
In order to get a slightly better handle on this question, we first need to distinguish clearly between the logical and physical levels of the system. Obviously the design goals are different at the two levels. At the physical level, redundancy will almost certainly exist in some shape or form. ...